Despite being one of the wealthiest people in the world, and despite protesting the unfairness of a tax system under which he pays a lower tax rate than his secretary does, Warren Buffett said in an interview a few year ago that he has filed for Social Security and cashes those monthly checks.
Social Security recipients got 2008 Economic Stimulus Payments under President Bush, but those ESP amounts had income ceilings, so Warren Buffett didn't get one of those.
Social Security recipients got 2009 Economic Recovery Payments--and, as far as I can tell--there were no income limits for ERP recipients, so I assume Warren Buffett did receive one.
And any 2009 ERP credit he did get is not going to change his 2009 tax liability (since he's clearly ineligible for Making Work Pay credits in any event), which means that he got that $250 ERP without any tax consequences whatsoever.
The difference is most likely pragmatic rather than ideological.
The 2008 ESP payments required millions of elderly and disabled Social Security recipients to file tax returns in order to get them. That caused a huge burden on the IRS, which had to redeploy auditors to answer the phones due to all the questions they got about the 2008 Economic Stimulus Payments.
So, determined not to make that mistake twice, it looks like Congress decided to have other government agencies (Social Security, RailRoad Retirement Board, and the Veterans Administration) do the stimulating this year. But, unlike the IRS, those agencies have no way to know the total amount of income their recipients receive, so they just sent those checks out to all their recipients--including Warren Buffett.